Improve memory allocation/consumption in the Stack of Open Elements

Instead of allocating new dictionaries for the scope elements, the scope
checks are just unrolled in-place. Now we have 6 almost identical methods
that differ only in the inline-check-method. Not optimal but minimal
memory and performance penalty.

This should reduce memory consumption and increase the performance
while parsing, see issue #10

Sources/include/HTMLStackOfOpenElements.h

@@ -163,11 +163,11 @@
  https://html.spec.whatwg.org/multipage/syntax.html#has-an-element-in-the-specific-scope
  */
 - (HTMLElement *)hasElementInScopeWithTagName:(NSString *)tagName;
-- (HTMLElement *)hasAnyElementInScopeWithAnyOfTagNames:(NSArray *)tagNames;
-- (HTMLElement *)hasElementInListItemScopeWithTagName:(NSString *)tagName;
-- (HTMLElement *)hasElementInButtonScopeWithTagName:(NSString *)tagName;
+- (HTMLElement *)hasHeaderElementInScope;
 - (HTMLElement *)hasElementInTableScopeWithTagName:(NSString *)tagName;
 - (HTMLElement *)hasElementInTableScopeWithAnyOfTagNames:(NSArray *)tagNames;
+- (HTMLElement *)hasElementInListItemScopeWithTagName:(NSString *)tagName;
+- (HTMLElement *)hasElementInButtonScopeWithTagName:(NSString *)tagName;
 - (HTMLElement *)hasElementInSelectScopeWithTagName:(NSString *)tagName;
 
 /**